Abstract
SummarySub-Saharan Africa is projected to see a 55% increase in food demand by 2035, where cassava (Manihot esculenta) is the most widely planted crop and a major calorie source. Yet, cassava yield in this region has not increased significantly for 13 yr. Improvement of genetic yield potential, the basis of the first Green Revolution, could be realized by improving photosynthetic efficiency. First, the factors limiting photosynthesis and their genetic variability within extant germplasm must be understood.Biochemical and diffusive limitations to leaf photosynthetic CO2 uptake under steady state and fluctuating light in 13 farm-preferred and high-yielding African cultivars were analyzed. A cassava leaf metabolic model was developed to quantify the value of overcoming limitations to leaf photosynthesis.At steady state, in vivo Rubisco activity and mesophyll conductance accounted for 84% of the limitation. Under nonsteady-state conditions of shade to sun transition, stomatal conductance was the major limitation, resulting in an estimated 13% and 5% losses in CO2 uptake and water use efficiency, across a diurnal period. Triose phosphate utilization, although sufficient to support observed rates, would limit improvement in leaf photosynthesis to 33%, unless improved itself.The variation of carbon assimilation among cultivars was three times greater under non-steady state compared to steady state, pinpointing important overlooked breeding targets for improved photosynthetic efficiency in cassava.
Highlights
Rising global population coupled with increased urbanization is predicted to increase food demand by 60% until 2050
Increasing yield depends on increasing genetic yield potential, i.e. the yield that can be achieved in the absence of pests, disease, water and nutrient limitations
CO2 uptake (De Souza & Long, 2018). While these results provided an indication that there was genotypic variation, they did not account for the full range of quantitative limitations of iew photosynthesis and indicated the need for evaluation of a larger number of farmer-preferred cultivars to provide a more realistic assessment of the photosynthetic limitations under steady-state conditions
Summary
Rising global population coupled with increased urbanization is predicted to increase food demand by 60% until 2050. Demand increase will be greatest in Sub-Saharan Africa where population is expected to double by 2050 (van Ittersum et al, 2016; United Nations, 2017). In this region, where cassava (Manihot esculenta Crantz) is the most planted crop (FAOSTAT, 2019a), food demand is projected to rise by 55% within just 15 years (World Bank, 2017). Dependence on cassava in Africa is underlined by the fact that it accounts for a higher proportion of food consumption per person than any staple in any part of the world (i.e., 0.4 kilograms per person/day) (Henry et al, 2004). Increasing yield depends on increasing genetic yield potential, i.e. the yield that can be achieved in the absence of pests, disease, water and nutrient limitations
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